"""往来单位服务：开单取价 + 信用额度。

取价优先级（quote_price）：
1. 客户专属价 CustomerProductPrice
2. 价格等级价 PriceLevel.discount_rate × 默认售价（rate>0 且 <1 时生效）
3. 最近成交价（该客户+商品最近一张已过账销售单行单价）
4. 默认售价 Product.sale_price
"""

from __future__ import annotations

from decimal import Decimal

from .models import Customer, CustomerProductPrice, PriceLevel


def quote_price(*, tenant, customer: Customer, product) -> dict:
    """返回 {price, source, last_price, min_price, max_price}。

    price 为基本单位价；last/min/max 为该客户历史成交参考（基本单位口径）。
    """
    # 1. 客户专属价
    cpp = CustomerProductPrice.objects.filter(
        tenant=tenant, customer=customer, product=product
    ).first()
    if cpp is not None:
        price, source = cpp.price, "customer"
    else:
        # 2. 价格等级价
        level: PriceLevel | None = customer.price_level
        rate = level.discount_rate if level else Decimal("0")
        if rate and Decimal("0") < rate < Decimal("1"):
            price, source = product.sale_price * rate, "level"
        else:
            # 3. 最近成交价
            last = _history(tenant, customer, product).first()
            if last is not None:
                price, source = last.unit_price, "last"
            else:
                price, source = product.sale_price, "default"

    hist = list(_history(tenant, customer, product).values_list(
        "unit_price", flat=True
    )[:50])
    return {
        "price": price,
        "source": source,
        "last_price": hist[0] if hist else None,
        "min_price": min(hist) if hist else None,
        "max_price": max(hist) if hist else None,
    }


def _history(tenant, customer: Customer, product):
    """该客户+商品的已过账销售行（新→旧）。"""
    from apps.sales.models import SalesBillLine

    return (
        SalesBillLine.objects.filter(
            tenant=tenant,
            bill__customer=customer,
            bill__state="confirmed",
            product=product,
        )
        .order_by("-bill_id", "-id")
    )


def credit_usage(*, tenant, customer: Customer) -> dict:
    """客户信用额度占用：{limit, outstanding, available}。

    limit=0 表示未启用管控；available = limit - outstanding（未启用时为 None）。
    """
    from django.db.models import Sum

    from apps.finance.models import Receivable

    agg = Receivable.objects.filter(
        tenant=tenant,
        customer=customer,
        status__in=["open", "partial"],
        is_deleted=False,
    ).aggregate(total=Sum("total_amount"), paid=Sum("paid_amount"))
    outstanding = ((agg["total"] or Decimal("0")) - (agg["paid"] or Decimal("0"))).quantize(
        Decimal("0.0001")
    )
    limit = customer.credit_limit or Decimal("0")
    return {
        "limit": limit,
        "outstanding": outstanding,
        "available": (limit - outstanding) if limit > 0 else None,
    }


def check_credit(*, tenant, customer: Customer, extra_amount: Decimal) -> dict:
    """下单/过账前检查额度。返回 usage；超限抛 CreditLimitExceeded。"""
    from apps.sales.services import CreditLimitExceeded

    usage = credit_usage(tenant=tenant, customer=customer)
    if usage["limit"] <= 0:
        return usage
    if usage["outstanding"] + extra_amount > usage["limit"]:
        raise CreditLimitExceeded(
            customer.code, usage["outstanding"], usage["limit"], extra_amount
        )
    return usage